ARCHIVED - Guidelines for the Prevention and Control of Meningococcal Disease

 

5.0 Diagnosis and Bacterial Typing

Laboratory confirmation of a clinical diagnosis of IMD is important for the identification and management of cases and outbreaks, as well as for regional and national surveillance and detection of epidemiologic trends over time. Meningococcal isolates from all IMD cases should routinely be sent to the provincial/territorial laboratory to ensure appropriate and timely monitoring of serogroups and for antibiotic susceptibility testing. Isolates are forwarded to the Public Health Agency of Canada’s National Microbiology Laboratory (NML) for further phenotypic typing and genetic analysis.

Culture of blood, cerebrospinal fluid (in the absence of contraindications to lumbar puncture) and other normally sterile sites is required for isolating bacteria for identification. Polymerase chain reaction (PCR) testing is available in several centres across Canada for rapid molecular diagnosis of meningococcal infection and serogroup identification on whole blood and cerebrospinal fluid. PCR has greater sensitivity than culture, particularly if there has been prior administration of antibiotics(8,25-27). Latex agglutination antigen testing may be a useful adjunct.

Several laboratory methods are used to track the epidemiology of N. meningitidis in Canada. The serogroup, serotype and serosubtype of the organism can be determined using antibody or by DNA sequencing of the responsible genes. Antigenic variation in proteins located in the outer membrane of the organism can be detected. For example, an isolate of N. meningitidis C:2a:P1.2 is of serogroup C, serotype 2a and serosubtype P1.2.

In addition, genotyping procedures can be done, such as multilocus enzyme electrophoresis (MLEE), multilocus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE). MLEE and MLST are most suitable for studying global molecular epidemiology. PFGE can be useful in discriminating strains of N. meningitidis within a population, particularly during a period of increased incidence of disease. Knowledge of PFGE patterns can be most useful for smaller populations in which the incidence of disease may be very high but there are only a few cases, and more discriminatory tests are required to determine whether these are unrelated cases caused by different strains or whether there is increased transmission of a particular strain.

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